Selenium rectifier



Aug. 16, w BLACKBURN ET 2,479,301

SELENIUM RECTIFIER Filed Nov. 29, 1947 .Steel WITNESSES: NVENTORS WayneE. Elackburn and fllbertBoY 12 Hpodaca Patented Aug. 16, 1949 SELENIUMRECTIFIER Wayne E. Blackburn,

berto R. Apodaca,

IIJIollywood, Calit., and Aluz signors to Westingl Savinon, Mexico, as-

ouse Electric Corporation,

East Pittsburgl, Pa., a corporation of Pennsylvania Application November29, 1947, Serial No. ?88,948 6 Claims. (Ci. 175-366) Our inventionrelates to dry-contact rectiflers or light-sensitive devices andparticularly to devices of this type which employ a layer of selemum.

One object of our invention is to provide a selenum rectifier orlight-sensitive device in which the surface of the seienium at which therectificaton or photo-electric eflect is produced is provided with -aboundary layer which insures a high resistance to current flow in thenominally non-conductive direction when an alternating voltage isimpressed upon it. such a layer may be referred to as a blocking layer.

Another object of our inventiou is to produce v on a selenium layer ablocking layer which has a high resistance to current flow in thenominally non-conductive direction but which does not introduce a highresistance to current flow in the nominally conductive direction.

Another object of our invention is to provide a seienium layer with ablocking layer which shall not undergo such chemical reaction during thepractical use of the device incorporating it that the latter will changeits electrical characteristics, or as it is sometimes termed will "ag ata deleterious rate in service.

Other objects of our invention will become apparent upon reading thefollowing description. taken in connection with the drawing in whichFigure 1 is a sectional elevation and Flg. 2 a top plan view of arectifler embodying the principles of our invention. e

Referring in detail to the drawing, the rectifler comprises a base-plateI which may comprise steel which has first been sand-blasted on thesurface 'and thereaiter nickel-plated. The plate I thus prepared ispreferably provided with a central hole 2 by which it may be mountedupon a spindle provided with means for rapidly rotating it. The plateand spindle while in rotation are dipped into molten seienium and thenwithdrawn therefrom. The centrifugal force removes all of the seieniumexcept a thin uniform layer 3 from the surface of the plate. The coatedbase plate is then submerged in a .01 normal water solution of thalloushydroxide at about C. The 'plates are removed in about 20 seconds andrinsed in distilled water at room temperature. No alkaline precipitateis left on the free seienium surface. It appears that the barrier layer4 is tormed by the chemical reaction of the thallous lon with theexposed selenium thus forming a continuous film of thallous selenide asthe new free surface. While the unit thus produced may next be annealedat the temperature of 185 c. and provided with a contact layer 5 of somelow meiting good conductor such as cadmium or one of the alloys ofcadmiun and tin, we prefer, in accordance with the process described incopending application Serial No. 509,817, filed November 10, 1943, inthe name of Wayne E. Blackburn, now Patent No. 2,447,630, granted August24, 1948.' to apply the said contact layer first to the thallousselenide surface and thereafter to anneal the unit by heating it to thetemperature of the order of C. for a suitable period, for example, fora, time between six and sixteen hours. The unit rectifier, when made inaccordance with the process just described, may then be connected toelectrical circuits in any of the st a dard connections for rectiflerdiscs.

We claim as our inventionz- 1. The method of producing an electricalsurface element which comprises producing a, surface of seienium andsolution of 0.01 normal concentration of thallous hydroxide.

2. The method of producing an electrical surface element which comprisesproducing a surface of seienium and immersing it in a water solution of0.01 normal concentration of thallous hydroxide at about 25 C.

3. The method of producing an electrical surface face of selenium andimmersing it in a water solution of 0.0.1 normal concentration ofthallous hydroxide for about 20 seconds.

4. The method of producng an electrical surface element which comprisesproducing a surface of selenium and immersing it in a water solution of0.01 normal concentration of thallous hydroxide at about 25" C. forabout 20 seconds.

5. An electrical circuit element comprising a base-plate having aportion of its surface coated with seienium, the surface of saidseienium being coated with thallous selenid and the surface oi' saidthallous selenide being provided with a cadmium counter-electrode.

6. A rectifler comprising a base-plate having a layer of seleniumthereon which is provided with a coating of thallous selenide, thesurface of said thallous selenide being provided with a cadnium contactlayer.

WAYNE E. BLACKBURN. ALBERTO R. APODACA.

REFEREN CES CITED UNITED STATES PATENTS Name Thompson et ai.

Number Date Oct. 24, 1944 immersing it in a water' element whichcomprises producing a sur-'

